An example of a conventional semiconductor physical quantity sensor of electrostatic capacitance type is shown in FIG. 8. As shown therein, an insulating glass substrate 2 is placed on an upper surface of a silicon semiconductor substrate 1 (hereafter referred to as silicon substrate), in which both substrates 1, 2 are bonded at peripheral areas thereof (joining areas) 5 by anodic bonding. The silicon substrate 1 is etched to form a frame-shaped support mounting 3 having a pressure-sensing portion 4 thin-walled relative thereto to be flexible and movable up and down. Each of the upper and lower surfaces of the pressure-sensing portion 4 serves as a movable electrode, while the glass substrate 2 above has a fixed electrode 7 formed on an inner surface thereof and facing the movable electrode. Now, an electrostatic capacitance is generated between the movable electrode and the fixed electrode according to a gap 6. The pressure-sensing portion 4 moves with a pressure applied thereto, thereby changing the gap 6, so that the electrostatic capacitance generated between both electrodes also changes. The change of the gap, namely pressure, is designed to be obtained by detecting the change of the electrostatic capacitance.
A signal is output to an external circuit via through-holes 8a, 8b formed in the glass substrate 2 from a conductive film 9a electrically connected to the silicon substrate 1 or movable electrode, and from a conductive film 9b which is electrically connected to the fixed electrode 7 through its lead portions 7c and insulated from the silicon substrate 1 by an insulating film 10. Note that reference numeral 11 designates a power supply for bonding the silicon substrate 1 to the glass substrate 2 by anodic bonding. The anodic bonding between the silicon substrate 1 and glass substrate 2 at the time of applying a high voltage for the bonding may cause a risk that the movable pressure-sensing portion 4 is moved by electrostatic attraction to get closer to the fixed electrode 7 formed on the glass substrate 2, generating discharge A therebetween, so that the fixed electrode 7 is alloyed by heat and thereby fusion-bonded to the pressure-sensing portion 4. The occurrence of such state leads to a problem that the pressure-sensing portion 4 becomes unmovable and unable to detect a pressure.
In order to solve this problem, it is known, as shown in FIG. 9 and FIG. 10, that on a glass substrate 2 in a sensor equivalent to the one described above, a short-circuit conductive pattern (equipotential wiring) 70 to electrically connect a fixed electrode 7 of the glass substrate 2 to a movable electrode of a silicon substrate 1 is formed in advance, and that when a high voltage is applied for anodic bonding, both electrodes are electrically connected via the equipotential wiring 70. This makes the fixed electrode equipotential to the silicon substrate in anodic bonding. Accordingly, discharge does not occur in anodic bonding, so that both electrodes are prevented from contacting and being fusion-bonded to each other, making it possible to obtain a high bonding strength as well. However, with the equipotential wiring being kept formed, desired sensor characteristics cannot be obtained.
Thus, it is known to form a short-circuit conductive pattern having a gap which electrically connects the fixed electrode to the silicon substrate via short-circuit conductive pattern in anodic bonding, and which electrically disconnects the fixed electrode from the silicon substrate in normal measurement of a physical quantity (refer e.g. to Japanese Laid-open Patent Publication Hei 9-196700). However, this short-circuit conductive pattern is formed between the glass substrate and the silicon substrate, which leads to a problem that bonding voids (condition like trapping bubbles preventing bonding) are likely to occur around the short-circuit conductive pattern.
It is also proposed to provide a short-circuit conductive pattern on a silicon substrate outside a bonding portion between a silicon substrate and a glass substrate, and to cut this short-circuit conductive pattern e.g. using a laser after anodic bonding (refer e.g. to Japanese Laid-open Patent Publication Hei 6-340452). However, in this case, a problem arises in that a chip size increases because the short-circuit conductive pattern is provided outside the bonding portion between both substrates.